The measurement of strain at elevated temperatures has previously involved one of two basic approaches, namely placing the sensing unit in the heated zone or transferring the specimen strain outside the heated zone to a sensing element at or near room temperature.
Problems encountered with having the sensing unit in the heated zone are; linearity/repeatability loss due to temperature effects on the sensing unit and complexities of cooling the sensing unit.
Prior devices using the alternate approach of transferring the strain mechanically outside the heated zone tend to be complex and include frictionally contacting components which contribute to hysteresis and non-linearity.
Most of the present extensometers have complex mechanisms for attachment to the specimen.